Ulnar Nerve
Motor Supply
All but five intrinsic hand muscles are innervated by the ulnar nerve. The remaining are innervated by the C8-T1 roots via the Median Nerve. The mnemonic AbOF can be used to remember which muscles are above the law in that they aren't innervated by the ulnar nerve: the abductor (Ab) and flexor (F) pollicis brevis, opponens pollicis (O), and lateral lumbricals.
Clinical Relevance
Importantly, the ulnar nerve doesn't provide sensation to the medial forearm. That is innervated by the Medial Antebrachial Cutaneous Nerve. Therefore, an ulnar lesion at the elbow results in anaesthesia of the ulnar hand and fingers, but not the forearm.
Nerve compression in the Guyon canal results in anaesthesia of the ventral palm and fifth finger. Dorsal sensation is supplied by the dorsal sensory branch of the ulnar nerve.